1. Field of the Invention
The present invention relates to a modular measurement device for example a measurement probe, for use on positioning apparatus such as a coordinate measurement machine, a machine tool, robots, non cartesian machines or the like.
2. Description of the Related Prior Art
Measurement probes are known (e.g. U.S. Pat. No. 5,404,649) which have a number of stylus modules releasably attachable to a sensor module for producing a signal indicative of the movement of the stylus module relative to the sensor module. A range of stylus modules are provided which have different lengths or configurations, allowing the probe to be used for different measurement tasks.
However, a sensor module that has to have a large range of styli is generally designed as a compromise and probing forces for each stylus used will be different. The sensor module has to be strong enough to support the stylus used and to allow movement of the stylus. If a short stylus is used and a sensor is designed for a longer stylus then the measurement device will be less than optimally sensitive. A plurality of sensor modules each of which is designed for use with just one stylus would be ideal, but is very expensive for the customer. U.S. Pat. No. 6,430,833 shows a separable sensor and stylus support mechanism. However, the use of a range of styli is not addressed.
The present invention provides a modular measurement device comprising: a retaining module attachable to a positioning apparatus; at least one stylus support module being exchangeably attachable to the retaining module; and at least one stylus module being exchangeably attachable to a stylus support module,
wherein the stylus support module has a suspension system for movably supporting the stylus module, wherein the retaining module and the stylus support module cooperate to measure displacement of the suspension system, and wherein the exchangeable attachment of the stylus module to the stylus support module is formed by complementary mountings on the stylus module and the stylus support module, allowing a repeatable rest position of the stylus module relative to the stylus support module following exchange.
Preferably the complementary mountings form a kinematic mounting. Preferably a plurality of stylus support modules and stylus modules are provided, the stylus modules are grouped and each group of stylus modules is configured such that it may be attached only to one of the plurality of stylus support modules.
Preferably each respective exchangeable attachment includes a magnetic attraction device.
Preferably the magnetic attraction force exerted by each respective attachment differs.
The invention provides also a modular measurement device comprising: a retaining module attachable to a positioning apparatus; a plurality of stylus support modules being exchangeably attachable to the retaining module; and a plurality of stylus modules being exchangeably attachable to a stylus support module,
wherein each stylus support module has a suspension system for movably supporting the stylus module, the retaining module and the stylus support module cooperate to measure displacement of the suspension system and the suspension system of at least one of the stylus support modules has a different configuration from that of at least one of the other of the stylus support modules.
Thereby embodiments of the invention provide for one sensor module which can have a range of styli attached thereto via a smaller range of styli support modules intermediate the sensor and the styli.
Preferably the suspension system includes spaced resilient elements and the different configuration includes a different spacing between the elements.
Preferably each stylus has a work contacting area and the degree of movement per unit force applied to the work contacting area of each stylus module is approximately equal when attached to a stylus support module.
Preferably the plurality of stylus modules are grouped and each group of stylus modules is configured such that it may be attached only to one of the plurality of stylus support modules.
Preferably the configuration of each group allows only one orientation of the stylus modules in the group relative to the stylus support module to which they are attachable. This means that a stylus module can be removed and replaced in the same place, giving better repeatability of measurement if stylus modules are removed and replaced.
Preferably the releasable attachments between the retaining module and the stylus support modules or between the stylus support modules and the stylus modules, forms a kinematic mounting.
Preferably the exchangeable attachments between the retaining module and the stylus support modules or between the stylus support modules and the stylus modules includes magnetic attraction.
Preferably there exists magnetic attraction between the retaining module and the stylus support modules, and between the stylus support modules and the stylus modules and the magnetic attraction is greater between the retaining module and the stylus support modules.
In use of modular measurement systems for example of the type mentioned above, it is often desirable to have machine driven exchange of various modules in the system. U.S. Pat. No. 5,404,649 shows such an arrangement.
If modules are stacked and held together by magnetic attraction it will be difficult to control the sequence of release of the stack e.g. when trying to remove the outer most module of the stack the inner most module might come away instead.
The invention extends also to a stacked modular measurement system having at least three modules in a stack held together by means of magnetic attraction between adjacent modules wherein the attraction between one pair of the adjacent modules is not equal to the attraction between another pair of adjacent modules.
Thus in embodiments of the invention the module at the free end will be removed before the module at the machine end if the stack is pulled at its free end. This allows a more simple routine for changing modules of the machine. In embodiments the invention allows simple movements to change modules when modules are stored on a rack on a measurement machine.
Preferably the stack has an end mountable to a machine and a free end and the module at the free end has less attraction to its adjacent module than the attraction of the module at the machine end and its adjacent module.
The invention extends also to a modular measurement system comprising a modular measurement device including: a retaining module attachable to a positioning apparatus; at least one stylus support module being exchangeably attachable to the retaining module; at least one stylus module being exchangeably attachable to a stylus support module, wherein the stylus support module has a suspension system for movably supporting the stylus module, the retaining module and the stylus support module cooperate to measure displacement of the suspension system and the exchangeable attachment of the stylus module to the stylus support module is formed by complementary mountings on the stylus module and the stylus support module allowing a repeatable rest reposition of the stylus module relative to the stylus support module following exchange, and the system further comprising a rack for storing any of the modules when not in use.
The invention extends also to a modular measurement system comprising a modular measurement device including: a retaining module attachable to a positioning apparatus; a plurality of stylus support modules being exchangeably attachable to the retaining module; a plurality of stylus modules having a work contact area and being exchangeably attachable to a stylus support module, wherein the stylus support module has a suspension system for movably supporting the stylus module, the retaining module and the stylus support module cooperate to measure displacement of the suspension system and the suspension system of each stylus support module has a different configuration, and the system further comprising a rack for storing any of the modules when not in use.